The first lady also spoke about increased support for military families in their daily lives. Earlier this week, President Barack Obama announced the new set of initiatives that will emphasize military children's education, military spouses' educations and careers, increased child care and quality of life improvement.
"You don't have to be a member of a military family or live near a base to help and reach out," the first lady said. "We can all do it in our own way. And one of the things I just tell people is to do what you do best."
Volunteering, offering professional services at no cost or hiring a veteran or military spouse were ways to help those who serve the nation's military, she said.
The first lady said the nation's response in the aftermath of the Tucson shootings was a clear demonstration of America's true spirit.
The Jan. 8 shooting rampage left six people dead and at least 12 others wounded.
Among the wounded were U.S. Rep. Gabrielle Giffords, who police say was the intended target of alleged shooter Jared Loughner. The dead include U.S. District Judge John Roll and 9-year-old Christina-Taylor Green.
Christina-Taylor's death demonstrated "just how fragile life is, and just how important it is for you to ... hold the ones you love just a little bit tighter, and value the things that are good in others. Not to take those things for granted. That's what times like these teach us," she said.
"Even in our deepest pain, our most horrific moments, we come together, because that community stepped up and supported Gabby Giffords and all the other families ... they were there for them. And the spirit of that is something that we, you know, we need to embrace and be reminded that that's who we are as a nation," the first lady said.
"That gives me the energy to do the next hard thing, because I know who I'm working for. I'm working for my country, you know?"
Living her life in the public eye brings its own challenges.
At the Jan. 19 state dinner in honor of visiting Chinese President Hu Jintao, the first lady's choice of dress designer got people talking.
Designer Oscar de la Renta said the first lady should have worn a gown from an American designer, rather than the show-stopping red gown from British designer Alexander McQueen.
The first lady has an answer for her critics.
"Look, women, wear what you love. That's all I can say. That's my motto. I wear what I like because ... I gotta be in the dress, so," she said, adding that it was a much better use of her time for her to focus on childhood health and rallying support for military families.
She also spoke highly of the legacy of Nelson Mandela, the legendary South African anti-apartheid activist. Mandela has been hospitalized and concerns about the aging statesman's health are mounting.
"What do you say about someone who's changed the face of the world? Nelson Mandela is, as so many of our heroes ... paved the way for people like me and my husband and so many other who are going to continue to look up to his legacy," she said. "So we are grateful to have been alive to see the impact of his life."
Throughout his life, Mandela has continued to champion patience and understanding.
"You know, not holding on to the past, and moving towards the future. It's still relevant today ... all over the world, these are lessons that we're still working on. But he's given us a life that has given us some guidance, it's given us a little road map about how to treat one another."